Why is Blender 2.8 slower than older versions?
Eevee is used as a "quick preview" of sorts for your render. That way you don't have to wait for Cycles to sample before you can actually see your render in full detail; Eevee is real-time.

As for your main question, have you tried un-installing Blender altogether, and re-installing the latest version of 2.8? 

If you have, it might be that you have 8GB of RAM and an i5 CPU. These are not the best performance-wise.